BugFix: undefined variable for layer 1/2 implementation
BugFix: undefined variable for layer 1/2 implementation

A variable (`enc_out`) was defined locally to an if block, while
another if block later was trying to use the same variable. This
bug only surfaced when using layer 1 or 2. Moved declaration of
`enc_out` to outside both if blocks as a fix.

fdalvi/nmt-repr-analysis,boknilev/nmt-repr-analysis,boknilev/nmt-repr-analysis